11. Sensors

Sensor framework:

• Determine which sensors are available
• What the sensor’s capabilities are
• Acquire raw sensor data
• Register/unregister sensor event listeners

Types:

• TYPE_ACCELEROMETER
  • Acceleration in m/s^2
  • Includes gravity
• TYPE_AMBIENT_TEMPERATURE
  • Not common
  • Room temperature in Celsius
• TYPE_GRAVITY
  • Software sensor
• TYPE_GYROSCOPE
  • Measures rate of rotation
• TYPE_LIGHT
  • Light level in lux
• TYPE_LINEAR_ACCELERATION
  • Excludes effect of gravity
• TYPE_MAGNETIC_FIELD
  • Ambient geomagnetic field in three axes
  • Measured in μT
• TYPE_PRESSURE
  • Ambient air pressure in hPa
• TYPE_PROXIMITY
  • Proximity of object
  • Usually binary
• TYPE_ROTATION_VECTOR
  • Orientation of device

Can Sensor capabilities:

• Minimum delay (in μS)
• Power consumption (in mA)
• Max range
• Resolution

Using sensor:

• Obtain SensorManager object
• Create SensorEventListener to listen to SensorEvents
  • Two methods
    • onAccuracyChanged(Sensor sensor, int accuracy)
    • onSensorChanged(SensorEvent event)
      • When sensor value changing
      • Should not do heavy computations in this method (or at least not on the same thread)
      • Don’t hold on to the event: it is part of a pool of objects and so the values may be altered
• Register the listener
  • Registration if for a specific sensor and sampling period
  • The sampling period is a suggestion/hint
    • Pre-defined constants: SENSOR_DELAY_ NORMAL, UI, GAME, or FASTEST
  • And unregister when done (e.g. onPause)

Sensor coordinate system:

• X-axis: parallel to the x-axis of the screen in the device’s natural orientation (may be landscape for tablets)
• Y-axis: parallel to the y-axis of the screen in the device’s natural orientation
• Z: normal to the screen, positive pointing towards the user